WASHINGTON (AP) – Republic of Georgia authorities, aided by the CIA, set up a sting operation last summer that led to the arrest of Russian man who tried to sell a small amount of nuclear-bomb grade uranium in a plastic bag in his jacket pocket, U.S. and Georgian officials said.

The operation, which neither government has publicized, represents one of the most serious cases of smuggling of nuclear material in recent years, according to analysts and officials.

The arrest underscored concerns about the possibility of terrorists acquiring nuclear bomb-making material on the black market, although there was no suggestion that this particular case was terrorist-related.

“Given the serious consequences of the detonation of an improvised nuclear explosive device, even small numbers of incidents involving HEU (highly enriched uranium) or plutonium are of very high concern,” said Melissa Fleming of the U.N.’s International Atomic Energy Agency.

Details of the investigation, which also involved the FBI and Energy Department, were provided to The Associated Press by U.S. officials and Georgian Interior Minister Vano Merabishvili.

Authorities say they do not know how the man acquired the nuclear material or if his claims of access to much larger quantities were true. He and three Georgian accomplices are in Georgian custody and not cooperating with investigators.

Georgian attempts to trace the nuclear material since the arrest and confirm whether the man indeed had access to larger quantities have foundered from a lack of cooperation from Russia.

Merabishvili said that he was revealing the story out of frustration with Russia’s response and the need to illustrate the dangers of a breakdown in security cooperation in the region.

A message left with the press office of the Russian Embassy was not returned. A duty officer at the Russian Foreign Ministry told The Associated Press that there was no one authorized to comment on Wednesday night.

Russia has tense relations with Georgia, a former Soviet republic. Georgia has been troubled by Russia’s support for separatists in two breakaway Georgian border regions, Abkhazia and South Ossetia.

The sting was set up after Georgian authorities uncovered extensive smuggling networks while investigating criminal groups operating in the breakaway republics, Merabishvili said.

“When we sent buyers, the channels through Abkhazia and South Ossetia began to expand and we started seeing a huge flow of materials,” he said. “Sometimes it was low-grade enriched materials, but this was the first instance of highly enriched material.”

According to his account, during an investigation in South Ossetia, a Georgian undercover agent posing as a rich foreign buyer made contact with the Russian seller in North Ossetia, which is part of Russia.

After the Russian offered to sell the sample, the agent rebuffed requests that the transaction occur in North Ossetia, insisting the Russian come to Tbilisi, the Georgian capital.

At a meeting in Tbilisi, the man pulled out from his pocket a plastic bag containing the material. Uranium has a low level of radioactive emission and can be transported more safely than other radioactive materials.

The man was arrested and sentenced to eight to 10 years in prison on smuggling charges. His accomplices were sentenced on lesser charges.

Russian authorities took a sample of the material but failed to offer any assistance despite requests for help from the Georgians, Merabishvili said.

“We were ready to provide all the information, but unfortunately no one arrived from Russia, not even to interview this person,” Merabishvili said. “It is surprising because it is in Russian interests to secure these materials. There are terrorist organizations in Russia who would pay huge amounts of money for this.”

The Georgians asked for U.S. assistance. Agents from the FBI and the Energy Department took the material back to the United States, where it was tested by the Energy Department’s National Nuclear Security Administration.

“The material was analyzed by agency nuclear experts and confirmed to be highly enriched uranium,” said Bryan Wilkes, a spokesman for the the agency.

Fleming, of the IAEA, said that the agency was aware of the Tbilisi seizure and was expecting formal notification from Georgia soon.

The CIA declined to comment on the case, while the FBI confirmed its involvement in the investigation.

Merabishvili, who was visiting Washington this week, said he did not have some details of the investigation available, including the exact date that the arrest was made or the full name of the suspect. Further efforts to clarify with the Georgian Embassy were not successful.

None of the U.S. officials would confirm the exact weight of the seizure or its quality, but Merabishvili said it was about 3.5 ounces of uranium enriched by more than 90 percent.

Uranium enriched at 90 percent is weapons grade.

A nuclear bomb of a design similar to the one exploded over Hiroshima in 1945 would require about 110 pounds of uranium enriched at over 90 percent, according to Matthew Bunn, a senior research associate who focuses on nuclear theft and terrorism at Harvard University’s Kennedy School of Government. Bunn said that a more sophisticated implosion type nuclear bomb would require 33 to 40 pounds.

According to an IAEA database, there have been 16 previous confirmed cases that either highly enriched uranium or plutonium have been recovered by authorities since 1993.

In most cases the recoveries have involved smaller quantities than the Tbilisi case. But in 1994, 6 pounds of highly enriched uranium intended for sale were seized by police in the Czech Republic. In 2003, Georgian border guards using detection devices provided by the U.S. caught an Armenian man with about 5 ounces of HEU, according to the State Department.

Fleming said that examples of stolen or missing bomb-grade nuclear material, including highly enriched uranium and plutonium, are rare and troubling.

David Albright, a former U.N. weapons inspector and head of the Washington-based Institute for Science and International Security said that lacking help from Russia, the CIA may be looking to other allies to help identify who has access to lost nuclear material.

“Russian cooperation in answering these questions is critical but it has not been forthcoming,” he said. “One way to identify who is active in trading these materials is to conduct sting operations,” he said.

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Associated Press writer Katherine Shrader contributed to this report.